The present invention relates to a key. More particularly embodiments of the present invention relate to a key resistant to breakage in operation.
The use of a mechanical lock operated by insertion of a matching key as a security mechanism is well known. Examples of locks in use today include the lever tumbler lock and the pin tumbler lock. Keys for a variety of locks are usually made from a metal or metal alloy and share a basic structure. At one end is a head portion (which may also be called the bow or grip) which is held by a user of the key to insert the lock-engaging portion at the other end (which may also be called the bit) into the lock, and to turn the key about its long axis to operate the lock mechanism by the lock-engaging portion. Depending on the type of lock and key, the head and lock-engaging portion may be joined by a shaft representing perhaps most of the length of the key (for example in a key operating a typical lever tumbler lock) or by a short joining section (for example in a key operating a typical pin tumbler lock).
A common problem in many locks, particularly in those exposed to the effects of weather or in those which are operated infrequently, is that the lock mechanism can partially or totally seize up. The increased resistance in the lock mechanism requires a user to apply more force to attempt to turn the key and operate the lock. The force applied to overcome the resistance of the lock mechanism produces stress in the key material. When the yield strength of the key material is exceeded, the key begins to deform plastically. The hardened metallic material making up a typical key will not deform far before it breaks. A similar situation may arise in which a user inserts a key in the incorrect lock in error and attempts to turn the key.
Frequently the break occurs near the point at which the key enters the face of the lock leaving the lock-engaging portion of the key in the lock. It may only be removed with difficulty, which usually requires the services of a locksmith. In the meantime the lock is immobilized and the key unusable.
United States patent number U.S. Pat. No. 6,196,036 describes a torque-limited key which includes a grip and a lock or latch engaging member. A torque-limiting device connects the grip to the engaging member. The torque-limiting device may include a spring, a frictional engagement, or any other type of resilient member. The torque-limiting device allows a torque applied to the grip to rotate the engaging member, so long as the applied torque is less than a predetermined level. If the applied torque exceeds the predetermined level, the grip will rotate relative to the engaging member in order to prevent breaking the engaging member off inside the lock or latch, and also in order to prevent damaging the mechanism of the lock or latch.
It would be desirable to provide a further solution to the above problem which does not require a key which contains a number of moving parts.